The objectives of the current research project are definition on a cellular level of the hyperplasia or hypertrophy occurring in the left and right ventricles, and the changes occurring in the lungs in puppies and adult dogs subjected to various volume overload situations by surgical creation of intracardiac or great vessel left-right shunts producing increased pulmonary blood flow. The definition of the relationship between pulmonary hypertension and the type of cellular response in the pulmonary vascular tree, together with correlation of cellular response with left ventricular function and performance in different animal age groups are further objectives of this project. The goals set out above are being achieved by the creation of left- to-right shunts at various levels in the heart or great vessels of puppies and adult dogs. Left ventricular function is studied prior to and immediately after the creation of these shunts by increasing left ventricular afterload with Angiotensin. For example, adult dogs have been shown, during the current study, to tolerate Potts anastomoses less well than puppies, and to show poor left ventricular performance in the immediate postoperative period when left ventricular afterload has been increased. The reasons for this difference in tolerance will be further examined and the adaptation of the left ventricle to shunts such as these studied with catheterization procedures 12 - 18 months following surgery. Ultimately, the hearts of each animal will be analyzed chemically (for protein, RNA and DNA) and pathologically in an attempt to explain these differences.